What is the difference between a planet and a planetesimal?

A planetesimal is a small celestial body that is believed to have coalesced from dust, rock, and other materials in the early solar system, eventually leading to the formation of planets. These bodies are typically smaller than planets and range in size from a few meters to several kilometers. On the other hand, a planet is a celestial body that orbits a star, is massive enough to be nearly spherical in shape, and has cleared its orbit of other debris.

The distinction between a planet and a planetesimal is based on their size, shape, and orbital characteristics. While planetesimals may have played a crucial role in the formation of planets, they are not considered planets themselves due to their smaller size and lack of orbital clearance.